1. Field of the Invention
This invention relates to a method of preparing a siloxane compound having olefinic unsaturation.
2. Description of the Prior Art
The reaction between compounds having aliphatically unsaturated carbon linkages such as C=C or C=C with silicon compounds having silicon-bonded hydrogen atoms in the presence of platinum to form new silicon compounds is well known in the art and is known as hydrosilation. A patent by John L. Speier and Donald E. Hook, U.S. Pat. No. 2,823,218, teaches that such reactions can be carried out in the presence of chloroplatinic acid. Speier et al. teach that both olefinic compounds and acetylenic compounds readily react to form new silicon compounds wherein the SiH adds across the unsaturated carbon bonds with a high product yield. Speier et al. also teach that the presence of other substituents in the unsaturated molecule, whether they be functional or entirely inert, does not prohibit the reaction. The unsaturated compounds which undergo reaction are taught as including unsaturated alcohols such as allyl alcohol, methylvinylcarbinol and ethynyldimethylcarbinol. Speier et al. teach that if an unsaturated alcohol is employed, a competing alcoholysis reaction will take place, but the reactants will no longer be those introduced where the source for the SiH is a silane, however, in general this problem does not arise when a siloxane is used as the source of SiH because the siloxanes are relatively inert to any extraneous substituents in the unsaturated reactant.
Speier et al. teach that the reaction temperature can vary over an extremely wide temperature range and optimum temperatures depend upon the concentration of catalyst present and the nature of the reactants. Temperatures suggested range from 0.degree.C. to below 300.degree.C. The temperature should be such that at least one of the reactants or a portion of the reaction mixture is in a mobile stage, liquid or gaseous and the maximum temperature is determined only by the stability of the reactants and the operator's desire to avoid decomposition products.
Speier et al. teach that the reaction time is variable and depends upon the reactants, reaction temperature and catalyst concentration among other things. Contact times of greater than 16 or 17 hours do no harm unless an extremely elevated temperature is employed, however, many reactants give a practically quantitative yield with contact times of 30 minutes or less and often an excellent yield can be obtained as soon as the exothermic reaction has begun which may be a matter of seconds. Speier et al. also teach that the reaction can be carried out at atmospheric, subatmospheric or superatmospheric pressures. The choice of conditions is a matter of logic based upon the nature of the reactants and the equipment available where non-volatile reactants are adaptable to being heated at atmospheric pressure with or without reflux and gaseous reactants at ordinary temperatures are preferably reacted at substantially constant volume under autogenous or induced pressure wherein the best results are obtained by maintaining at least a portion of the reactants in the liquid phase.
Speier et al., as well as others, have been concerned with obtaining addition products from the reaction of aliphatically unsaturated compounds and silicon compounds having silicon-bonded-hydrogen atoms. However, none have suggested that there are situations where the product of such a reaction is an inhibitor for the very reaction by which it is made. Thus, the reaction begins but as soon as a small amount of product is produced the reaction stops because the products inhibit the reaction by poisoning the catalyst.
The present invention is directed to a preparation of a unique class of compounds which inhibit the catalyst at low temperatures but not at high temperatures. Because the catalyst which is inhibited is used to make the inhibiting compound, the preparation method to provide a commercially suitable process was not obvious. The inhibiting compounds are a class of siloxane compounds containing olefinic unsaturation and are prepared from acetylenic alcohols and siloxane compounds having silicon-bonded-hydrogen atoms. The earliest work did not produce an inhibiting compound for the platinum catalyzed addition of aliphatic unsaturation to silicon-bonded hydrogen, but instead provided a complex mixture which may be called "a crosslinker-catalyst-inhibitor." This work is the subject of a copending application Ser. No. 528,962, filed Dec. 2, 1974, entitled "Crosslinker-Platinum Catalyst-Inhibitor and Method of Preparation Thereof" by Randolph G. Niemi filed on even date herewith and assigned to the same party.
Niemi combined polysiloxane having multiple silicon-bonded hydrogen atoms, a platinum catalyst and an acetylenic alcohol, heated the mixture for about 16 hours at 70.degree.C. and obtained a complex mixture after removing unreacted acetylenic alcohol by reduced pressure at room temperature, which when mixed with vinyl containing siloxane polymers remained uncured at room temperature but would cure at elevated temperatures. Thus, Niemi had found one could make room temperatue stable compositions from his mixture, but for each composition a separate mixture of crosslinker, catalyst and acetylenic alcohol was required. Attempts to separate the complex mixture into various components were impractical and expensive. The product could not be characterized to identify any particular species which were responsible for the inhibiting effects on platinum catalysts.
Using the method of Niemi, Chi-Long Lee and Ollie W. Marko as described in a copending application Ser. No. 528,966, filed Dec. 2, 1974, entitled "Olefinic Siloxanes As Platinum Inhibitors" filed on even date herewith and assigned to the same party prepared specific olefinic siloxane compounds which were inhibitors for the platinum catalysts in the addition reaction between aliphatic unsaturation and silicon-bonded hydrogen atoms. For example, Lee and Marko mixed equal molar quantities of ##EQU1## and EQU (II) (CH.sub.3).sub.3 SiO{(CH.sub.3)HSiO}.sub.3 Si(CH.sub.3).sub.3
with a catalytic amount of a platinum catalyst from 2 to 50 parts per million platinum, heated the mixture at 70.degree.C. for 16 hours, stripped off the unreacted starting ingredients, left set over night and then vacuum distillation was used to recover the product. The product was an olefinic siloxane compound of the formula ##EQU2## This compound mixed with a vinylsiloxane polymer, a silicon-bonded hydrogen containing compound and a platinum catalyst did not cure at room temperature in 10 days but when heated to 150.degree.C. the composition cured in 2 minutes. Thus, this compound is a platinum catalyst inhibitor at room temperature, but not at elevated temperature.
Although Lee and Marko were able to characterize specific inhibitor compounds, the method of preparation was impractical. The process provided only a low conversion from 2 to 20 percent and the yield was less than 5 percent after distillation. In addition to both low conversion and yield, the reaction was difficult to control and could become violently exothermic, thus creating a safety hazard.
To improve the process, Lee and Marko discovered that the inhibitor could be prepared in a gas liquid chromatographic column as described in a copending application Ser. No. 528,959, filed Dec. 2, 1974, entitled "Method of Preparing Olefinic Siloxane By GLC" filed on even date herewith and assigned to the same party. Lee and Marko coated the injection port of a GLC column with a layer of platinum catalyst, heated the port at 350.degree.C. and injected a mixture of (I) and (II) while maintaining the column at 300.degree. to 400.degree.C. The product (III) was obtained in yields of from 30 to 35 percent. This process had advantage over the Niemi process in that less platinum catalyst was used, very short residence times down to 1 to 2 seconds were needed, the yields were higher, high purity product was obtained and separate distillations were not needed. However, the method was not suitable for the production of large amounts of olefinic siloxane inhibitor. When larger GLC columns were used the yields decreased and the column became plugged by gelled materials. Thus, for small scale operations this method was found suitable but was deficient for large scale production.